What does this relay do?

[JamesSchu]

Can anyone tell me what the relay pictured does? It comes on when the heating or hot water starts.

The relay is breaking down - clicking for minutes rather than a couple of seconds – and needs replacing.


It is connected to what an electrician friend tells me is a 4in fan PCB board (slight scorching on the board). The wiring from here then goes into another electrical box feeding the timer clock, x2 zone valves and a pump.


My friend doesn’t have time to come over due to work commitments but says it’s unusual – and two of his electrician colleagues have looked at pictures of it and neither have seen anything like it before. Two plumbers have looked at it and neither wanted to touch it.


An instruction on the electrical box says “white: trig”, which I presume to mean trigger, but for what? The house is approx 20 years old.


Despite the relay clicking for a long time, everything appears to be working as it should be.

 

[Gasguru]

What a rats nest, it all needs ripping out and doing properly.
That fan timer is badly designed and has cooked as a result.
Perhaps someone tried to make a pump overrun...but that's guesswork.
Start with working out all the wiring and go from there.
What's the boiler make and model?

 

[ericmark]

I would guess with the electronics some form of run on device, I remember my first house had hot air gas central heating which the flue was long and went through the car port, and there was a flap to detect when the flue extractor was running and it was linked to the boiler so flue motor started then the boiler fired up.

There is also pump run on systems to cool boiler down on switch off, used when boiler designed for c plan or y plan but being used with s plan, as with s plan the motorised valves default shut, but with c plan no motorised valve and y plan default is DHW on.

I will admit I have when younger done things like shown, but as I have progressed in the trade have realised if you want some one else to work on it latter either good plans or standard systems are the way to go.

Clearly a socket back box and blanking lid, so the board does seem pre-made and if you can read the number on the chip it will help working out what it does, I would guess 556 or 76212 or other timer chip.

 

[JamesSchu]

Yes, I agree, it needs doing properly. Boiler is a Halstead VBX18

 

[SFK]

Not suggesting using a new board (although that resistor looks way past its best and a fire risk) - follow advice of others above.

That is a 'run on board', designed for big fans (not sure about pumps).
This is the replacement of your board, and this has the relay on the board.
https://www.ebay.co.uk/itm/Fan-over...217901?hash=item23cd89d62d:g:jUcAAOSwR-9dxVnI
https://www.ebay.co.uk/itm/Adjustab...535606?hash=item1aa3940176:g:jiYAAOSwPeJfYyo7

OPERATION of QF-RD21F
When 240vac connected to L2 the green LED is illuminated and power is supplied from L2 to FAN.
When 240vac is removed from L2 the green LED starts flashing and power is supplied from L to the fan for the over-run time that has been set.
Lifetime: 100,000 movements
Max 10A switching at 240Vac

SFK

 

[ianmcd]

Your boiler is a Halstead Eden, you dont need that home made mess for anything, just get it wired correctly

 

[Harry Bloomfield]

Yes, I agree, it needs doing properly. Boiler is a Halstead VBX18

It looks like a 4000 series CMOS IC utilised as some sort of timer circuit. The large resistor, which is failing due to heat and age, looks like it has been used as a mains dropper for a low voltage supply for the electronics. As others have suggested, probably a run on timer for the pump, though it could also be a boiler inhibitor to prevent the boiler rapid cycling.

Replacing that large failing resistor with a new higher rated on and fixing any heat damage on the PCB, might well resolve the relay clicking on and off issue, but is it worth the effort? It is around 30 years old judging by the components, so probably time your entire heating control system was updated.

[EDIT] That is a modern boiler, so will include direct control of the pump from the boiler, so no need for any separate timers. It just needs to be properly wired.

 

[JamesSchu]

Thanks for the replies. Yes, I'm waiting on an electrician to call me back. I want it all ripping out and doing safely/properly. As for age of components, house is only 20 years old. I imagine it was fitted when new as we've lived here 14 years and it hasn't been done in my time.

 

[Harry Bloomfield]

Thanks for the replies. Yes, I'm waiting on an electrician to call me back. I want it all ripping out and doing safely/properly. As for age of components, house is only 20 years old. I imagine it was fitted when new as we've lived here 14 years and it hasn't been done in my time.

The timer system is a DIY install, an add on for perhaps the original boiler. You can check the likely age of the timer device by reading the code on that IC. They are all marked with a year and week of manufacture.

 

[durhamplumber]

Yes, I'm waiting on an electrician to call me back.

Don't hold your breath.

 

[Harry Bloomfield]

You might be better inviting an heating engineer, who is familiar with the electrical side, than an electrician.

 

[ericmark]

When I bought this house, I looked at the central heating wiring mess, and simply ripped it out and started from scratch, however I selected summer months to do that, not heart of winter. The wiring is clearly not to IET regulations with cores being visible outside the socket back boxes.

You might be better inviting an heating engineer, who is familiar with the electrical side, than an electrician.

I am not sure a heating and ventilation engineer would be any better than an electrician or plumber, likely all will do what I did and rip out and start again. The problem is time, it may be possible to repair but to do in a way to comply with regulations could cost more than ripping out and starting again. To fix that you can end up chasing ones tail, remember a DIY man can simply get it to work, but the professional needs to get it to work safely. Even if he can get it to work, he could not leave it in that state. A days labour is not cheap, and I know I would be worried as to if the client would pay me for the time spent correcting such a lash up.

I would not want to squeeze it in, I would want time available so I can be sure not to have to walk away leaving no heating, really that is a summer job, were it does not matter if not fixed that day you can return next day. Best repaired by a firm with multi-tradesmen than any sole trader at this time of year, so they can stay and complete and don't have to rush away to next job.

Most electrical firms will have a guy who works as a trouble shooter, he spends all his time fixing the odd non run of mill fault, and as a result he gets really good solving the unusual, that's all he does, but the sole trader often does not come across enough weird systems to really get to know how to fix them, there are the exceptions of course, but I would aim for a firm, rather than a sole trader.